1. Field of the Invention
This invention relates to monitoring systems for monitoring the operation of a device, and more particularly to a sensor plug for mounting sensors for use with such systems.
2. Related Art
In the ever-increasing competition in the industrial field, industrial equipment, such as rotating machinery, must operate at or near full capacity and sustain such operation for long periods of time. With this type of demand placed on such equipment, periodic maintenance to avoid a catastrophic failure becomes important. Of course, periodic preventative maintenance requires that the equipment be taken off-line for service, thereby potentially resulting in unnecessary down time. Maintenance engineers have been challenged to establish proper time intervals for scheduled preventative maintenance in order to reduce such unnecessary down time.
Alternatively, some maintenance engineers have concluded that the equipment should operate until catastrophic failure. This stems from the fact that, in some instances, it may be better to operate equipment until it fails than to accept the maintenance and the resulting penalty costs of shutting down the equipment prematurely. Also in lieu of scheduled maintenance, some defects may be found by a trained operator. Because such detection is subject to human interpretation, pass/fail criteria may vary between operators and also from day to day with the same operator. Other defects may not be detected at all.
Attempts have been made to automatically monitor such equipment for defects through the use of a sensing element disposed within the equipment itself or through the use of a hand-held device which is periodically attached to one or more discrete locations on the machine being monitored. More sophisticated monitoring systems are permanently installed and carry out essentially continuous monitoring of a machine-mounted transducer along with computer-based analysis of all monitored data.
Most automatic monitoring systems typically sense vibration or temperature. Vibration is produced by the moving parts in the rotating machinery due to causes such as unbalance, misalignment of shafts, worn out bearings, broken gear teeth or foreign particles lodged within the machine. Excessive levels of vibration indicate malfunction of the machine, which can result in machine failure. The temperature of a bearing, for example, can also be monitored to detect the occurrence of over-heating. In some instances, the oil level in the machine may be monitored, automatically through the use of a float system or manually through the use of a dipstick or a sight glass, so that the likelihood of defects or malfunction of the device due to low oil level may be reduced. Other automatic means to detect oil level include beam techniques that measure time of flight or frequency modulation of an ultrasonic, microwave or light/laser beam. Electrical methods have also been employed that detect changes in current, voltage, capacitance or inductance of the liquid to determine the fluid level.
The above-mentioned monitoring systems have certain disadvantages. For example, the sensor may be located remotely from the monitoring unit. This is undesirable for a number of reasons. First, the wire harness between the monitor and the sensor is rather complex. In addition, the wire harness itself must be protected by passing the harness through an armored braid or a metal or plastic conduit to prevent damage or destruction.
Another disadvantage of the prior systems with regard to oil level detection is that the resulting measured value is often inaccurate, especially when utilizing a sight glass or a dipstick. With float-type oil level sensors, the apparatus is rather complex and occupies a relatively large amount of space within the oil reservoir of the machine.
In addition, the ability to retrofit existing equipment with the new monitoring system is limited. Because the sensor is remotely located from the monitor, installation is difficult, time-consuming, expensive and may require a skilled operator to ensure all connections are properly made.
One feature of the invention is an add-on or built-in component to a device, such as a gearbox, to allow conditions within and around the device to be monitored in order to reduce failures in service, optimize maintenance costs, and provide operating condition information that overcomes the above and other disadvantages of conventional monitoring systems. In one particular aspect of the invention, a sensor plug for use in sensing a plurality of operating conditions of a device is disclosed. The sensor plug includes a plug body and a probe end formed at one end of the body. The probe end is adapted for mounting to the device. A plurality of sensors is also included in the sensor plug and is located within the body. Each sensor senses an operating condition of the device. Accordingly, advantageously, the sensor plug may be adapted for mounting to an existing device or may be adapted for installation during manufacture of the device. Additionally, locating one or more sensors in a sensor plug advantageously provides for ease of mounting the sensors to the device.
In one embodiment, the sensor plug includes a well formed at an end of the body opposite the probe end. At least some of the sensors are located within the well. In another embodiment, the sensor plug further includes a pressure port extending from the well through the probe end. A pressure sensor communicates with the pressure port. The pressure sensor may also communicate with ambient pressure. Thus, differential (gage) pressure may be detected. In another embodiment, the sensor plug may include a temperature port extending from the well to the probe end. A temperature sensor is disposed within the temperature port. The temperature port is adapted to position the temperature sensor to sense oil temperature or case temperature of the device. In an alternative embodiment, the temperature port extends through the probe end and a temperature port plug is inserted into and extends partially within the temperature port. This effectively seals the probe end such that fluid is prevented from leaking through the temperature port. In a preferred embodiment, the temperature port plug is formed of a thermally conductive material. The sensor plug may also include a vibration sensor. The vibration sensor may be mounted in the well to detect vibration in the device.
In another embodiment, the well of the sensor plug is filled with a potting material to encapsulate the sensors. An ambient pressure port may be formed through the potting material so that pressure sensor may communicate with the ambient pressure. In a preferred embodiment, the sensor plug also includes a retainer for retaining the potting material within the well. Preferably, the well defines an axially extending sidewall having the retainer formed therealong for axially retaining the potting material within the well. In one instance, the sidewall is formed with a coarse surface, thereby defining the retainer. Alternatively, the sidewall may include a radially inwardly extending lip to define the retainer.
The sensor plug may also include a shoulder formed between the probe end and the well. The shoulder is adapted to axially support a housing for a processing unit such that the well may extend into the housing. When attached thereto, the leads from the sensors emerging from the well are connected directly to the processing unit mounted within the housing, thereby enclosing each lead entirely within the housing. A seal may also be disposed adjacent the shoulder for sealing against the housing. In a preferred embodiment, the shoulder is positioned in a spaced relationship with respect to the case of the device and the probe end so as to support the housing in a spaced relation away from the sidewall of the device.
In an embodiment of the invention, the probe end is adapted for communication with an oil reservoir of the device. Preferably the probe end is adapted attaching to an oil drain hole.
In another embodiment, the body is formed of at least one material selected from the group consisting of metal, plastic and ceramic.
In yet another aspect of the invention, the sensor plug includes a plug body adapted for mounting to the device and a support formed on the plug body. The support is adapted for mounting a housing for a processing unit to the sensor plug.
Various embodiments of the present invention provide certain advantages and overcome certain drawbacks of the conventional techniques. Not all embodiments of the invention share the same advantages and those that do may not share them under all circumstances. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.